Leicester Tigers have been drawn with former winners Cardiff Blues and Pau in next season's European Challenge Cup.
The Tigers failed to qualify for the Champions Cup following a dismal Premiership season where they finished one place above relegated Newcastle.
Geordan Murphy's side will also take on Italians Calvisano in Pool 5.
Wasps, who won this competition in 2003, will play Edinburgh and French duo Bordeaux-Begles and Agen.
London Irish have been handed a difficult draw on their return to European competition. The promoted Championship club will take on three-time European champions Toulon, Scarlets, and Bayonne.
Worcester and the Dragons face a trip to Siberia to play Enisei-STM in Pool 1, while Bristol Bears will play Stade Francais, Brive, and Zebre.
2019/20 Challenge Cup draw
Pool 1: Castres, Worcester Warriors, Dragons, Enisei-STM.
Pool 2: Scarlets, Toulon, London Irish, Bayonne.
Pool 3: Wasps, Edinburgh, Bordeaux-Begles, Agen.
Pool 4: Stade Francais, Bristol Bears, Zebre, Brive.
Pool 5: Cardiff Blues, Leicester Tigers, Pau, Calvisano.